Isomers of C.sub.2 H.sub.2 F.sub.4 (HFC-134s) are used as refrigeration fluids for a number of applications. HFC-134s can also be used as starting materials for producing various other halogenated hydrocarbons. Products containing isomers of C.sub.2 H.sub.2 F.sub.4 are produced in various degrees of isomer purity. One method of producing HFC-134s is by the hydrogenolysis of C.sub.2 C.sub.12 F.sub.4 isomers (CFC-114s). In the manufacture of C.sub.2 Cl.sub.2 F.sub.4 by the chlorofluorination of perchloroethylene the product typically consists of a mixture of the isomers, CClF.sub.2 CClF.sub.2 (CFC-114) and CF.sub.3 CCl.sub.2 F (CFC-114a) (see e.g., U.S. Pat. No. 4,605,798). If the CFC-114s are then used to produce CHF.sub.2 CClF.sub.2 (HCFC-124a), CF.sub.3 CHClF (HCFC-124), HFC-134 or HFC-134a by hydrodehalogenation, the products often consist of a mixture of C.sub.2 HClF.sub.4 and C.sub.2 H.sub.2 F.sub.4 isomers (see e.g., GB 1,578,933).
It has been found that for many applications, the presence of the second isomer of the isomer pair can significantly alter the physical and chemical properties of the desired isomer. For example, variation in the HFC-134/HFC-134a ratio in the product can result in dramatic variability in the thermodynamic properties critical for use in refrigeration applications. For use as a raw material feed, the presence of the unwanted isomer can result in yield loss due to increased side reactions. As a result, there has been a continually increasing demand for high isomer purity materials. Consequently, the separation of HFC-134 isomers represents a significant aspect of preparing these compounds for various applications.
Purification of halogenated hydrocarbon products has been the subject of considerable research. Of particular interest are the challenges presented in separating desired halogenated hydrocarbon products from materials such as impurities in the starting materials used to produce the halogenated hydrocarbon, excess reactants, and reaction by-products and/or reaction co-products which are difficult to remove by standard separation methods such as distillation. Selective sorbents such as carbons and zeolites have been proposed for various separations. The effectiveness of separation using such sorbents varies with the chemical components and the sorbents involved. The successful design of sorbent based systems is considered highly dependent upon experimental determination of whether the relative sorbencies of the particular compounds are suitable for such systems.
HFC-134 has a boiling point of -23.degree. C. and HFC-134a has a boiling point of -26.5.degree. C. Distillation is consequently relatively inefficient as a means for separating these two compounds.